Diesel vehicles may be equipped with aftertreatment systems which may include, for example, selective catalytic reduction (SCR) systems, diesel oxidation catalysts (DOC), and diesel particulate filters in order to reduce emissions. In some examples, turbocharged engines may include pre-turbocharger catalysts, e.g., a diesel oxidation catalyst, in the exhaust system at a position upstream of a turbine in the turbocharger system. Such a pre-turbo catalyst may attain its operating temperature, e.g., light-off temperature, more quickly than downstream catalysts and may extract little energy from the exhaust gas thereby interfering minimally with supplying exhaust energy directly to the turbine section of a turbocharger. Pre-turbo metallic catalysts may include two parts—the substrate and the mantle. The substrate, on which the reactive agent (washcoat) resides, may be made from very thin steel that is held by an outer casing of thicker steel (the mantle).
The inventors herein have recognized that, in some examples, it may be advantageous to mount a pre-turbo catalyst in a turbocharger, e.g., in a throat of a turbine in the turbocharger. However, mounting pre-turbo catalysts in a turbocharger may be difficult as the turbine scroll is usually as-cast. This means that a gap may need to be maintained between the mantle of the pre-turbo catalyst and the housing of turbine in order to reduce vibrations between the mantle and the turbine housing. Such vibrations may lead to degradation of the pre-turbo catalyst, e.g., the mantle may crack. However, since the mantle may change shape due to thermal loading, this gap may be difficult to maintain, resulting in vibrations between the mantle and the turbine housing and component degradation.
In one example approach, in order to address these issues, a turbocharger for an engine comprises a turbine and a catalyst substrate mounted directly within the turbine.
In this way, the mantle mounting may be removed from the pre-turbo catalyst and instead the substrate may be mounted directly into a pre-machined turbine housing. Because the substrate is spring-like in nature, it may better accommodate the changing shape of the turbine housing than a rigidly mounted version with a mantle. For example, the substrate could be mounted against a machined edge of the turbine or possibly even as-cast depending on process variation and clamped using a turbine/manifold gasket. Deleting the external mounting of the pre-turbo catalyst allows the substrate to flex with the turbine housing, thus reducing unwanted component vibration and degradation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.